FIG. 1 illustrates a portion of a UMTS wireless communication network. As shown, user equipment (UE) wirelessly communicates with a Node-B serving the communication needs of a geographic area (often referred to as a cell or collection of cells). The UE may be a mobile phone, wireless equipped PDA, wireless equipped laptop, etc. The Node-B is often referred to as a base station in other communication standards. The Node-Bs communicate with a radio network controller (RNC). The RNC routes, for example, data between Node-Bs or on to another communication network such as the internet.
Communication from a Node-B to a UE is referred to as downlink or forward link communication, and communication from a UE to a Node-B is referred to as uplink or reverse link communication. In the uplink, various communication channels may exist.
In the UMTS uplink, a EDCH (Enhanced Dedicated Channel) is used to provide high-speed scheduled data service. In the EDCH, a distributed scheduling approach is taken where scheduling decisions are made at each Node-B and communicated to the UEs. A Node-B scheduler allocates the TFI (transport format indication) or TFC (transport format combination) that a UE can use, based on the available rise-over-thermal (RoT) target of a cell. Two types of rate scheduling approaches are supported in UMTS. In relative rate scheduling, a UE sends a 3 stage rate request relative to its current rate, based on its power limit and buffer status. The Node-B scheduler makes scheduling decisions and sends a relative rate grant (RG) message. In absolute rate scheduling, each UE reports its power limit and buffer status to the Node-B. The Node-B determines the allowed peak transmission rates and sends either the peak TFI or the peak traffic-to-pilotratio (TPR) that a UE can use for EDCH communication.
The 3GPP contributions “Reference Node-B scheduler for EUL,” TSGR1#35(03)1246, 3GPP TSG RAN WG1, Qualcomm, Lisbon, Portugal, November 2003., and “Description of EUL scheduler,” TSGR1 Rel-6 Ad-hoc(04)0698, 3GPP TSG RAN WG1, Samsung, Cannes, France, June 2004., describe scheduling algorithms based on a greedy filling of available RoT. These scheduling methods compute a priority function based on the requested rate and the average rate of the UEs. The scheduler grants the right to transmit starting from the highest priority UE or user, then, successively to the lower priority users. However, this method may penalize high-priority users, when the available RoT is smaller than what is required to support all the users rate requests.